Field of the Invention
The present invention relates to an optical system and is suitable as an imaging optical system used in an imaging apparatus such as a silver-halide film camera, a digital still camera, a video camera, a digital video camera, a monitoring camera, and a broadcasting camera, for example.
Description of the Related Art
It is required that the imaging optical system used in the imaging apparatus have high optical performance across an entire image area and that various aberrations thereof be corrected in an excellent manner. The imaging optical system is also required to have an image stabilizing mechanism for inhibiting deterioration in image due to an effect of vibration such as a camera shake at the time of shooting. As the image stabilizing mechanism, a method of correcting variation in image position caused by the camera shake and the like by moving a part of lens units of the optical system in a direction including a component perpendicular to the optical axis is known.
It is known that the image stabilizing mechanism is used in a retrofocus-type wide-angle lens in which a focal length of an entire system is shorter than a back focus.
In order to obtain excellent optical performance by correcting an image shake at the time of vibration of the optical system, it is important to arrange the image stabilizing mechanism in an appropriate position of the imaging optical system.
U.S. Pat. No. 5,917,663 discloses that the wide-angle lens including a lens unit with negative refractive power and a lens unit with positive refractive power in order from an object side performs image stabilization by rotational movement of two positive lenses on a side closest to an image around a point on the optical axis.
Therefore, an incident position of a principal ray of an off-axis ray incident on an image stabilizing lens unit becomes high and there is a tendency that image-plane variation occurs at the time of the image stabilization in the off-axis ray and aberration correction at the time of the image stabilization becomes difficult. Also, the incident height of the off-axis ray incident on the image stabilizing lens unit becomes high and there is a tendency that coma aberration variation becomes large at the time of the image stabilization and the optical performance is deteriorated. Therefore, it is difficult to realize a large aperture ratio of the wide-angle lens disclosed in U.S. Pat. No. 5,917,663.
In order to correct the image shake at the time of the vibration of the optical system while maintaining the excellent optical performance, a lens configuration and refractive power of the image stabilizing lens unit are important and it is also important to arrange the image stabilizing lens unit at an appropriate position in an optical path.
An object of an embodiment of the present invention is to provide an optical system capable of easily obtaining a high-quality image across the entire image plane and of easily maintaining the excellent optical performance also at the time of the image stabilization with a wide angle of view and the large aperture ratio.